Since GaN-based light emitting diodes were first developed, GaN-based LEDs have been used for various applications including natural color LED displays, LED traffic signboards, white LEDs, and the like.
Generally, a GaN-based light emitting diode is formed by growing epitaxial layers on a substrate such as a sapphire substrate, and includes an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. In addition, an n-electrode pad is formed on the N-type semiconductor layer and a p-electrode pad is formed on the P-type semiconductor layer. The light emitting diode is connected to an external power source through the electrode pads and driven thereby. In this case, current flows from the p-electrode pad to the n-electrode pad through the semiconductor layers.
On the other hand, a flip-chip type light emitting diode is used to prevent light loss due to the p-electrode pad while improving heat dissipation efficiency, and various electrode structures are proposed to promote current spreading in a large area flip-chip type light emitting diode. Examples are disclosed in U.S. Pat. No. 6,486,499. For example, a reflective electrode is formed on the P-type semiconductor layer, and extension legs are formed on a region of the N-type semiconductor layer, which is exposed by etching the P-type semiconductor layer and the active layer, to facilitate current spreading.
The reflective electrode formed on the P-type semiconductor layer reflects light generated from the active layer to improve light extraction efficiency and helps current spreading in the P-type semiconductor layer. On the other hand, the extension legs connected to the N-type semiconductor layer help current spreading in the N-type semiconductor layer to allow uniform generation of light in a wide active region. Particularly, a light emitting diode having a large area of about 1 mm2 and used for high power output requires current spreading not only in the P-type semiconductor layer but also in the N-type semiconductor layer.
On the other hand, a forward voltage Vf is supplied to the light emitting diode to generate light, and a light emitting diode having good luminous efficacy refers to a light emitting diode capable of emitting the same intensity of light at a lower forward voltage. Therefore, various attempts have been made to decrease forward voltage of the light emitting diode.
On the other hand, in a process of dicing light emitting diodes on a wafer into individual light emitting diodes, an insulation layer exposed to a plane to be cut is likely to suffer from cracks. Such cracks can propagate into the light emitting diode. Moreover, interlayer delamination occurs due to cracks, thereby causing delamination of the insulation layer from semiconductor layers. Accordingly, moisture and contaminants can infiltrate the light emitting diode along an interface between the insulation layer and a semiconductor layer, thereby contaminating the light emitting diode, and delamination force with respect to layers in the light emitting diode can be reduced, thereby causing deterioration in reliability of the light emitting diode.